JPS6116074B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention comprises a first panel and a second panel provided at a predetermined distance from the first panel, at least one of these panels is a transparent body, and the first panel has a a first main electrode is fixed to the second panel, a second main electrode is fixed to the second panel apart from the first main electrode, and at least one color of pigment is disposed between the first and second main electrodes. an opaque insulating liquid in which particles are suspended, a majority of these pigment particles are unipolarly charged, and a layer of some kind is fixed at least partially on the second main electrode; Specifically, the present invention relates to an electrophoretic display device in which a third electrode is interposed between the first main electrode and the second main electrode so as to be separated by this layer. Electrophoretic displays are passive displays in which images or patterns are formed by the electrophoretic movement of particles. A simple electrophoretic image display device (hereinafter abbreviated as EPID device) is known from US Pat. No. 3,688,106. This known EPID device has pigment particles suspended in an organic liquid sandwiched between two electrodes, and at least one of the electrodes is transparent. In one embodiment, the pigment particles are negatively charged relative to the organic liquid. When a positive potential is applied to one electrode in the suspension, the pigment particles are attracted to that electrode. Particles are repelled when a negative potential is applied to the electrode. To create such an EPID device, one electrode panel is made by coating a transparent substrate, such as glass, with a layer of transparent conductive material. When light-colored pigment particles are attracted to the transparent electrode panel, the viewer sees the bright color reflected by the pigment particles through the transparent electrode panel. A dark dye is dissolved in a suspension, and in the background of the device, the pigment particles are hidden by the opaque dye, and the viewer sees only the dark color reflected by the dye. When the polarity of the electrode potential is reversed, the positional relationship of the colors is reversed. Also described in this U.S. patent specification
The EPID device has a "memory effect". Close the lid,
This is because even when the applied voltage is removed from the electrodes, the pigment particles remain in their old positions due to chemical, electrical or Van der Waals forces. However, EPID devices such as those described above are impractical for certain applications. This is the case when displaying a matrix. This is because the EPID device described above does not have a constant threshold value for switching when moving pigment particles from one side of the device to the other. The lack of such a sharp threshold characteristic in a matrix display results in long address times and a troublesome half-selection problem.
In such a matrix display device, there is a half-selected state in which one of the associated horizontal electrodes or vertical electrodes is selected although it is not addressed, and the corresponding display element receives about half of the applied voltage. However, due to the broad threshold voltage of the pigment particles in such a display element, only some of them cross the device, resulting in significant fluctuations in the displayed information. “Digest of the
"Recent Progress In" included in "Society for Information Display" (held in San Diego, California, May 1974).
The paper entitled "Electrophoretic Displays"
EPID devices with primitive control grids have been reported. According to the paper, this control grid is a "wire grit" that is electrically insulated from the two electrode surfaces and placed between them, where the A electrode is normally connected. About 1/
A positive voltage of 2V is applied as a bias voltage.
As far as the literature (particularly FIG. 5) is concerned, this primitive structure has no X-Y addressing function. Furthermore, although a threshold is certainly created by the structure shown in the paper as a very simple diagram, it is not possible to produce an electrophoretic display device that can be marketed with good reproducibility. It should be noted that an EPID device of the type mentioned at the beginning of this specification is known from U.S. Pat. The value is enhanced by additionally providing on one electrode a resistive layer whose resistance varies non-linearly with voltage. In order to match the resistance of this additional resistive layer, whose resistance varies non-linearly with voltage, to the resistance of the electrophoretic suspension, this additional resistive layer has a resistor at the intersection of the column and row electrodes. Point-shaped electrodes are provided at certain positions. The size of this point electrode must be chosen such that the capacitance of the additional resistive layer, whose resistance depends non-linearly on the voltage, matches the capacitance of the electrophoretic liquid. However, even with such a configuration, an electrophoretic display device with good reproducibility that can be sold on the market cannot be manufactured. It is an object of the present invention to provide a simple electrophoretic display and/or recording device that is X-Y addressable. Another object of the invention is to provide a control and switching device for varying the spatial distribution of pigment particles within an electrophoretic suspension. Yet another object of the invention is to provide an electrophoretic color display that can be addressed at low voltages and at relatively high speeds. According to the present invention, in the electrophoretic display device of the type described at the beginning of the specification, the above-mentioned certain layer is an insulating layer, the above-mentioned third electrode is used as a control electrode, and the above-mentioned first main electrode and the second selectively adjusting the electric field between the main electrode and establishing a threshold;
The present invention is characterized in that the pigment particles are moved depending on the direction of the electric field, and an image is formed on the main electrode depending on the presence or absence of the pigment particles. Preferably, the first electrode is a continuous layer provided on the first panel and the second electrode is comprised of a plurality of parallel strips. Preferably, the third control electrode is constructed by disposing a plurality of parallel stripes on the insulating layer so as to intersect with the parallel stripes of the second electrode. The parallel strips of the second electrode and the parallel strips of the third electrode form the column and row electrodes of the matrix, respectively, and are separated by an insulating layer. Preferably, the third electrode and the insulating layer are provided with a large number of uniformly distributed holes through which the pigment particles can migrate. According to the invention, pigment particles that are not addressed but are in a display element associated with a selected row electrode or a selected column electrode are not moved across the display; This is because the electric field between the second electrode and the third electrode holds the pigment particles associated with the semi-selective display element within the third electrode and the holes formed in the insulating layer. Note that the dimensions of the holes are 10 to 50 μm, and the distance between the centers of the holes is 15 to 60 μm. The invention will be explained with reference to the drawings. FIG. 1 is a partially cutaway and enlarged view of the EPID device of the present invention. FIG. 1 not only shows the structure of the EPID device of the present invention, but also serves to explain its manufacturing method. As shown in Figure 1, the EPID device of the present invention has a thickness of
Starting from a first flat panel or substrate 10 of 1.5 mm glass or clear plastic.
A plurality of parallel transparent conductive strips are fixed to the main surface of the substrate 10 to form column electrodes 11 . Column electrodes 11 are made of indium oxide, typically applied and fixed to substrate 10 by sputtering. In this example, the column electrodes 11 typically have a thickness of 3000 Å and a width of 2.5 mm. The length of the column electrodes 11 depends on the size and dimensions of the display device itself. Next, the substrate 10 and the vertical electrodes 11 are bonded to a thickness of 5 to 50 μm.
It is covered with an insulating layer 13 of photoresist or other dielectric of m. This is done by dip coating. Next, a row electrode 14 consisting of a plurality of parallel strips extending perpendicularly to the column electrodes 11 is fixed onto the upper surface of this insulating layer 13. This transverse electrode 14
is made of aluminum and is adhered to the insulating layer 13 by vacuum evaporation, and is spaced at least partially from the column electrode 11 via the insulating layer 13. The thickness of the transverse electrode 14 is approximately 700 Å, and the width is 2.5 mm.
shall be. The space 12 between the row electrodes 14 is the same as the space 12 between the column electrodes 11, but 25~
The width shall be 100μm. In one embodiment of the invention, the transverse electrode 14 and the insulating layer 1
A minute pocket or hole 18 is made in each of the holes 3 and 3. This is partially enlarged and shown in Figure 2. The hole 18 is omitted in FIG. 1 to avoid complicating the drawing. Note that the holes 18 are formed after the transverse electrodes 14 are fixed by vacuum deposition. In that case, first, a photoresist layer (not shown) is applied on the entire surface of the horizontal electrode 14.
A photomask with the desired pattern of pockets or holes is placed over the photoresist layer and the photoresist is exposed. The photomask is then removed, the photoresist is developed, and holes are made in the photoresist layer in the exposed areas.
A transverse electrode 14 extends below it. Next, an aluminum etching solution is applied to the photoresist layer in which the holes are uniformly formed, and the exposed portions of the horizontal electrodes 14 are removed. The insulating layer 13 remains bare underneath. The remaining photoresist layer is then removed using standard methods in the prior art. Then, the transverse electrode 14 with uniform holes appears in a bare state. The insulating layer 13 below the hole of the transverse electrode 14 must then be removed. If the insulating layer 13 is made of a photoresist layer, this process is simple, and the perforated horizontal electrodes 14 can be used as they are as a photomask for exposure. When the insulating photoresist layer 13 is thus exposed and developed (ie, decomposed), holes 18 are formed corresponding to the holes of the horizontal electrodes 14. This hole 18 is extended until it reaches the column electrode 11. A second flat panel 17 is then provided parallel to the first flat panel or substrate 10.
Covering the main surface of the second panel 17 with an electrode layer 16,
It is made to face the first panel 10. This electrode layer 16
is a continuous transparent electrode layer of indium oxide approximately 3000 Å thick and is adhered to the main surface of the second panel 17 by sputtering. A space of approximately 40 μm is provided between this continuous transparent electrode layer 16 and the aforementioned column and row electrode groups. Then, the peripheral edges of the first panel 10 and the second panel 17 are sealed (see FIG. 4), and a liquid is poured between them. In the region between the column electrodes 11 and the continuous transparent electrode layer 16, soluble dyes and colored pigment particles are uniformly dispersed and suspended in a conductive liquid such as xylene or perchlorethylene (tetrachlorethylene). A colloidal solution or suspension consisting of
9) is filled with an "electrophoretic liquid" (the above colloidal solution and the like will hereinafter be referred to as "electrophoretic liquid" throughout the present specification and claims). All particles suspended in the electrophoresis liquid are charged to the same sign (polarity), which can be achieved by adding a charging aid to the electrophoresis liquid. In addition, the first
The operation of the EPID device having the structure shown in the figure will be explained in detail later with reference to FIG. FIG. 2 shows a partially enlarged view of the insulating layer 13 and the horizontal electrodes 14. A large number of holes 18 are formed in the insulating layer 13 and the horizontal electrodes 14 by photolithography.
are densely and evenly spaced. Although the hole 18 may have any shape, it is shown in FIG. 2 as a circle for simplicity. However, in the later cross-sectional drawings, for convenience of explanation, the shape of the hole 18 is assumed to be square. In any case, in a typical case the hole 18 will be a square of approximately 20 .mu.m on a side or a circle of 20 .mu.m in diameter, but in general terms the dimensions will be between 10 and 50 .mu.m. The distance between the center of one hole and the center of the next hole is 15 to 60 μm. The hole 18 is the transverse electrode 14
In addition, the insulating layer 13 is completely penetrated so that the column electrodes 11 are exposed to the electrophoretic liquid. In this way, the transverse electrode 14 functions as a control grid. The pores 18 thereby function as physical potential wells through which the pigment particles can move in response to an applied electric field.
The area occupied by the holes 18 should be at least 50%, typically 60-70%, of the surface of the transverse electrodes. FIG. 3 is an enlarged cross-sectional view taken along the - line in FIG. 2. In this cross-sectional view of FIG. 3, the column electrodes 11 extend in a continuous layer on the first panel 10 in the left-right direction. An insulating layer 13 and a transverse electrode 14 are bonded thereon with physical potential wells or holes 18 thereon. FIG. 4 is a simplified representation of the EPID device of the present invention, with two column electrodes visible at the top and bottom.
The drawing shows a substrate 10 and two column electrodes 11 (Y ₁
and Y ₂ ), and the insulating layer 1
3 and a transverse electrode 14 are depicted. The second panel 17 extends parallel to the substrate 10 and has an electrophoretic liquid 19 between them. A continuous transparent electrode 16 is fixed to the second panel 17 as a back electrode. Note that FIG. 4 shows the present invention.
Also shown is a spacer/seal 28 (this can be made of synthetic resin) provided for the purpose of sealing and storing the electrophoretic liquid 19 between the substrate 10 and the second panel 17 in the EPID device. ing. Note that the thickness relationship between each electrode or each layer in FIG. 4 is not drawn to scale. Hole 18 is drawn in a highly exaggerated manner for clarity of illustration. Note that the pigment particles 20 are located at the holes 18 on the upper side of the drawing.
It is shown attracted to a transparent back electrode 16 at the bottom of the figure. The electrical connections for operating the EPID display are also only shown in highly schematic form. For simplicity, the continuous transparent back electrode 16 is
Although the transparent back electrode 16 is shown grounded, a positive or negative voltage may be applied to the transparent back electrode 16 depending on the operating mode.
The first column electrode Y ₁ is shown connected to the first switch 23 and the second column electrode Y ₂ is shown connected to the second switch 22 . The transverse electrode 14 is also connected to a voltage source, but is not shown in FIG. 4 to simplify the drawing. As will be explained in detail later, by changing the polarity of the row electrodes 14 and the column electrodes 11, the pigment particles 20 can be attracted to the column electrodes 11, or conversely be repelled from the column electrodes 11 and attracted to the transparent back electrode 16. .
This allows a desired image to be formed in an appropriate area of the EPID device. FIG. 4 is a highly schematic illustration of the visual effects of EPID operation. Either side of the EPID device can be used for image display. This is the fourth
In the figure, observer 1 and observer 2 are illustrated on both sides. The observer 1 will see the color of the dye through the transparent first part 24 of the second panel 17. This is because the electrophoresis liquid 19 is opaque and the pigment particles are hidden when the lid is closed. In the second part 25 of the second panel 17 , the pigment particles 20 drive the dye in the area of the transparent back electrode 16 , and the observer 1 can see through the second part 25 of the second panel 17 the pigment particles 20 .
You will see the color of One embodiment of the invention uses a bright yellow pigment. Note that this EPID device has a "memory effect". This is because the pigment particles remain on or near the electrode due to electrical forces, chemical forces, and van der Waals forces even after the applied voltage is removed. The observer 2 sees the color of the pigment through the upper side 26 of the substrate 10 and at the lower side 27 of the substrate 10.
Since the dye is present adjacent to the substrate 10, the observer 2 sees the color of the dye through the substrate 10. 5, 6 and 7 show one particular transverse electrode 1
4 and one single EPID corresponding to column electrode 11
The movement of the pigment particles 20 is shown during the "reset", hold-during-write, and write operating conditions of the device. These Figures 5, 6 and 7 are highly schematic representations of the transparent back electrode 16, the electrophoretic liquid 19, and the electrophoretic liquid 19 under the action of an electric field.
The pigment particles 20 (indicated by arrows) moving within, the single control or row electrode 14, the insulating layer 13 (not to scale), a portion of the single column electrode 11 and the substrate 10 have been greatly enlarged. It is depicted in the condition. 5, 6 and 7 show that when various predetermined voltages are applied to the transparent back electrode 16, the control electrodes or row electrodes 14 and the column electrodes 11, the pigment particles 20 move along the lines of electric force caused by the voltages. Electrophoresis liquid 19
It shows the trajectory that will be drawn within the
It is based on a theoretical calculation using the geometry of the EPID device (i.e., the thickness of the insulating layer 13 and the diameter, depth, and isolation state of the physical potential well 29) presented in the embodiment of FIG. It is based on a computer simulation of the movement of particles under an external electric field. FIG. 5 shows the "reset" operating condition. In this case, it is assumed that the pigment particles 20 were on or near the transparent back electrode 16 in the previous display operation state. The first thing that must be done to display the new information is to move all the pigment particles 20 into the holes 18 (here shown as physical potential wells 29).
This involves erasing previous information and "resetting" the device. It is assumed that the pigment particles 20 are negatively charged in this "reset" operating state and in the operating states shown in FIGS. 6 and 7. This can also be done with known techniques as described in US Pat. No. 3,612,758. In the reset operating state, a positive voltage of, for example, 10V is applied to the column electrode 11 (which is at the bottom of the physical potential well 29). On the other hand, the control electrode or transverse electrode 14
is set to approximately 0V. A negative pulse voltage of, for example, -10V is applied to the continuous transparent back electrode 16. If it is desired to increase the operating speed, the absolute values of these applied voltages may be increased. As a result, the pigment particles 20 move along their respective trajectories away from the transparent back electrode 16 and enter the physical potential well 29, as shown in FIG. reach To perform X-Y addressing, a display element is "selected" by applying predetermined voltages to the row and column electrodes corresponding to the display element to be activated. At this time, if it is not desired to activate other display elements related to either the "selected" row electrode or the "selected" column electrode, the previous state should be maintained. To do this, these display elements must be placed in a "half-selected" state by placing the device in a "hold" operating state. Note that the "half-select" state itself is also referred to as the "hold" operating state (hold-
It is also called "during-write". FIG. 6 illustrates the above-mentioned "hold" or "half-select" operating state, in which the column electrodes 11 (designated Yk) are used for X-Y addressing of the EPID cell array. ) is not selected, while the transverse electrode 14 shown (labeled
Add Xi. ) is selected. This "half-select"
In this state, the pigment particles 20 remain within the physical potential wells 29. As already pointed out in the description of the prior art, being able to create this "half-selected" state is of great significance when implementing XY addressing. Although no writing should be done in this half-selected state, for display elements located along either the selected row electrode or column electrode, the row electrode 14 and the column electrode 11
A potential difference of 10V will be applied between the two. This potential difference of 10 V is sufficient to create a hold state and hold the pigment particles in the display element in the semi-selected state within the physical potential well 29 as shown in FIG. In this "hold" operating state, a positive pulse voltage of, for example, 38V is applied to the transparent back electrode 16. However, because of the 10 V potential difference between the control or row electrodes 14 and the column electrodes 11, as described above, the pigment particles 20 are confined within the physical potential wells 29. Note that the two pigment particles 20 in FIG. 6, which are representative of the pigment particles 20 within the physical potential well 29, are subject to a pulling force that pulls them deeper into the physical potential well 29. In the write operation state shown in FIG. 7, the same pulse voltage is applied to the desired row electrodes 14 and column electrodes 11 corresponding to the display element to be written, or a pulse voltage more positive than the pulse voltage applied to the column electrodes 11 is applied. By applying a voltage to the control or transverse electrode 14, the electric field that confined the pigment particles 20 within the physical potential well 29 is erased or reversed. The pigment particles 20 then move across the cell toward the transparent back electrode 16 due to the 35 V potential applied to the transparent back electrode 16. The pigment particles 20 gather in a region on the transparent back electrode 16 corresponding to the intersection of the row electrode 14 and the column electrode 11. As a result, X-Y
When the selected display element is viewed from the transparent back electrode 16 side, it appears to be the color of the pigment particles, and when viewed from the substrate 10 side, it appears to be the color of the dye. Therefore, according to the present invention, any desired display element within the XY matrix can be selected and written to by the transverse electrode 14, which is the control electrode, without affecting any other display elements. In that case, the address time refers to the time required for the pigment particles 20 to move from the bottom of the physical potential well 29 to a point on the control electrode 14 for any display element. There is no need to wait for the pigment particles 20 to travel through the entire thickness of the cell before writing other display elements. Some operating characteristics of the EPID device of the present invention are listed in the table below.

Table: The EPID device of the present invention is very bright and has high contrast under normal ambient light levels, and the contrast remains high over a very wide range of viewing angles in bright ambient light. Figures 8a and 8b are highly simplified diagrams of how X-Y addressing is accomplished for multiple display elements within an EPID device of the present invention. FIG. 8a shows that the EPID cell or display element is connected to voltage sources 29 and 30. FIG. The figure shows, as an example, how to connect to the voltage source when activating the display element [R ₄ C ₃ ] located at the intersection of the fourth row and the third column. FIG. 8b schematically shows the result of the display element [R ₄ C ₃ ] selected at this time lighting up. The dashed lines on Figure 8b are shown for reference only. One technique used to form a character image on a display screen is to scan a plurality of display elements, during which time appropriate display elements are sequentially selected and activated to produce the desired image. It is to form a character image. Because the number of scan lines is finite and each display element is scanned at a speed that is imperceptible to the eye, the eye sees each active display element in its entirety at once; The entire character, consisting of a large number of active display elements, appears to be drawn at once. FIG. 9 is a highly simplified block diagram of a decoding circuit and a driving circuit of an EPID device that can be used in one embodiment of the EPID device of the present invention.
The character the user wants to display is on the keyboard 31.
Enter. A decoding circuit 32 is connected to the keyboard 31 and decodes specific characters on the keyboard 31 to activate specific rows and columns of the XY display. For this purpose, the output terminal of the decoding circuit 32 is connected to a column drive circuit 33, which drives the appropriate column electrode 11 of the EPID device corresponding to the particular column designated by the decoding circuit 32; Transverse drive circuit 3 with another output terminal
4 to drive the appropriate row electrode 14 of the EPID device corresponding to the particular row specified by the decoding circuit 32. A switch 35 with an erase function and a switch 36 with a write function are connected to a sequencing circuit 37, and appropriate signals are sent from the sequencing circuit 37 to the column drive circuit 33 and the row drive circuit 34. Then, these drive circuits 33 and 34 are activated in the correct order. A sequencing circuit 37 is also connected to a continuous electrode drive circuit 38 to activate the continuous transparent back electrode 16 of the EPID device.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of the EPID device of the present invention;
Figure 2 is an enlarged perspective view of a part of the transverse electrodes and insulation layer of the EPID insulating layer in Figure 1, and Figure 3 is a cross section of the EPID device taken along the - line in Figure 2. Figure 4 shows the present invention having two transverse electrodes.
Vertical cross-sectional view of a simple embodiment of an EPID device, No. 5
The figure is a highly enlarged schematic illustration of the movement of pigment particles during the "reset" operation, FIG. 6 is a similar illustration during the "hold" or "half-select" operation, and FIG. Similar illustrations during a "write" operation, FIGS. 8a and 8b are highly simplified diagrams showing how to X-Y address the multiple display elements of the EPID device of the present invention; FIG. FIG. 2 is a very simplified block diagram showing a decoding circuit, a driving circuit, etc. for correctly drawing an image on the EPID display elements arranged in a Y matrix. 1, 2... Observer, 10... Substrate (first panel), 11... Column electrode, (Y ₁ ... First part, Y ₂ ...
...Second part), 12...Space, 13...Insulating layer, 14...Transverse electrode, 16...Continuous transparent back electrode layer, 17...Second panel, 18...
Hole, 19... Electrophoresis liquid, 20... Pigment particle, 2
1... Ground point, 22... Switch, 23... Switch, 24... First part of second panel, 25...
Second part of second panel, 26... Upper side of substrate 10, 27... Lower side of substrate 10, 28... Spacer and seal, 29... Physical potential well, 31... Keyboard, 32 ... decoding circuit, 33 ... column drive circuit, 34 ... row drive circuit, 35 ... erase switch, 36 ... write switch, 37 ... ordering circuit, 38 ... continuous electrode drive circuit.

Claims (1)

[Scope of Claims] 1. A first transparent panel, and a second transparent or opaque panel spaced apart from it by a predetermined distance, the first panel having a first transparent panel. fixing a main electrode, fixing a second main electrode to the second panel apart from the first main electrode;
An opaque insulating liquid in which pigment particles of at least one color are suspended is placed between these first and second main electrodes, and the majority of these pigment particles are charged unipolarly, and the liquid is charged onto the second main electrode. an electrophoretic display in which a certain type of layer is at least partially adhered to said first main electrode and said second main electrode, and a third electrode is interposed between said first main electrode and said second main electrode, separated by said layer; In the device, the certain layer is an insulating layer, and the third layer is an insulating layer.
The first main electrode and the second main electrode are used as control electrodes.
selectively adjusting the electric field between the main electrode and establishing a threshold and moving the pigment particles depending on the direction of the electric field, depending on the presence or absence of the pigment particles. an image is formed on the main electrode, the first main electrode is formed of a continuous layer, the second main electrode is formed of a plurality of parallel strips, and the third electrode is formed of a continuous layer. a plurality of parallel stripes disposed on the insulating layer in a direction intersecting the parallel stripes of the second main electrode; 1. An electrophoretic display device, characterized in that the pigment particles are made to move through the pores, which are distributed throughout the pores. 2. The electrophoretic display device according to claim 1, wherein the dimensions of the holes are 10 to 50 μm, and the distance between the centers of the holes is 15 to 60 μm. 3. The electrophoretic display device according to claim 1, wherein the insulating layer has a thickness of 6 μm to 50 μm. 4. The electrophoretic display device according to claim 1, wherein the third electrode is an aluminum electrode.